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Why Won’t My Lawn Mower Stay Running? 8 Possible Reasons

red lawn mower in the field

Getting a lawn mower started can be a tricky task, especially if the mower is old or has been sitting for a while. It is always a relief when the engine turns over, and you hear the roar. However, that relief can quickly sour if the engine runs for a few minutes and then stops again. Engine stalls are common problems for lawn mower owners, but the causes are not as well understood as starter issues.

There are multiple reasons why your engine might not keep running after starting. Some problems are simple and only take a few minutes to resolve. Other problems are more serious and might require more in-depth solutions. Here are eight possible reasons your lawn mower might not stay running after starting.

divider 7 The 8 Possible Reasons Why Your Lawn Mower Won’t Stay Running

1. Old Fuel

Old fuel can cause a lawn mower to stall quickly after starting. Many people let their lawn mowers sit in their garages for long periods of time, which causes the gasoline to get stale and eventually go bad. Bad fuel will cause excessive sputtering and stalling when your lawn mower tries to get running.

Gas starts getting stale after three months and starts going bad after six months. Many people do not start their lawn mowers during the winter, so their engines sit for months at a time. Old fuel is a common problem during the spring when people are getting their small engines back in working order.

When restarting your lawn mower after a long break, you should always get brand new gasoline. If you left gasoline in the engine for months, it might become necessary to bleed the old fuel out of the engine and replace it with new fuel. Once the old fuel is gone, the mower will stop stalling.

2. Clogged Carburetor

clogged carburator of old lawnmower
Image By: kwanchai.c, Shutterstock

A clogged or dirty carburetor can also cause a lawn mower to start but then stall during use. A dirty carburetor can prevent the combustion in the engine from occurring properly, which will cause the engine to stall out. You can clean, unclog, and adjust the carburetor fairly easily.

Consult your owner’s manual for proper instructions on how to adjust your carburetor. Carburetors can be cleaned off with special sprays designed to break down persistent grime. A clean carburetor will cause your mower to run much more smoothly and will help prevent future stalls.

3. Choke Left On

Accidentally leaving your lawn mower’s choke on for too long can cause problems with the fuel mixture. The choke only needs to be used to start a cold engine and should be turned off as soon as the engine warms up. Failing to turn the choke off during use can cause your engine to stall.

You can also leave the choke on when the mower is sitting. This will cause the fuel in the engine to become concentrated and airless. Concentrated fuel will burn differently than well-aerated fuel, which can cause your engine to cut out after it starts. Sometimes, it is necessary to drain the fuel from the lawn mower in order to reset the fuel balance and prevent the mower from stalling.

4. Dirty Spark Plugs

Changing lawn mower spark plug
Image Credit: The Toidi, Shutterstock

Many people think that dirty spark plugs only prevent an engine from starting, but they can also prevent an engine from running properly. An engine with dirty spark plugs will have decreased amounts of power which can cause the engine to stop running if it encounters a situation where it needs more power than it can provide.

Spark plugs are easily cleaned. Make sure to disconnect the spark plugs before working on them to prevent getting an electrical shock. You can buy spark plug cleaner at your local home improvement store. If you are unsure about the proper procedure, consult your owner’s manual.

5. Dirty Air Filter

A dirty air filter is a common cause of lawn mower engine stalls. Air needs to be able to flow into the engine to fuel the combustion process. If the filter is full, it will prevent air from flowing into the engine at full capacity, which can cause low power, sputtering, and stops. Lawn mower air filters are extra prone to get clogged because mowing creates a ton of small clippings and debris that get sucked up into the air filter.

The best way to deal with a dirty air filter is to buy a new one and completely replace the old one. Look at your owner’s manual to find out what type of air filter your lawn mower takes and source a new one. Replacing the air filter should be simple once you have the right one. If you can’t replace the air filter, you can try and clean it off with water and a clean rag. Knocking off the largest of the debris will help get air flowing to the engine once more.

6. Old Grass Is Clogging The Blade

Red Old mower in the garden
Image Credit: David Schwimbeck, Shutterstock

If a lawn mower’s blade cannot spin, it will usually stop the mower from functioning. This prevents vital components in the mower from burning themselves out in the case of an obstruction. If the blade tries to spin but is stuck, it can cause components in the engine to deteriorate rapidly. To prevent this, there is a cut-off that trips when the blades can’t spin freely. This is a common reason for stalling. Check under your mower for signs of debris or old grass. There could be leftover clippings along the outer edge of the blade housing that can cause the blade to slow during use.

7. Air Vents Are Clogged or Dirty

Gas engines need a steady supply of air to keep running. If the airflow slows down or stops, it can cause the engine to stall out quickly. Small engines have a multitude of small vents to let air flow into the engine where it is needed. These vents can occasionally get clogged with dirt and grass clippings which will hamper the flow of necessary air to the engine. These vents can easily be hosed off or brushed off to clear them of debris and are one of the reasons why it is important to clean off grass clippings and old grass from the mower when you are finished using it.

8. Fuel Lines Are Clogged Or Dirty

Rusty old lawnmower
Image Credit: Steve Lovegrove, Shutterstock

If there is something impeding the flow of gasoline from the gas tank to the engine, it will cause the lawn mower to stall out during use. Sometimes dirt or grime can enter the fuel line and cause the gas to slow down to a trickle or even stop flowing. If the engine runs out of gas supply, the lawn mower will stall.

You can clean the fuel lines by carefully disconnecting them from the carburetor and flushing them out. You should also check for holes, cracks, or build up in the lines to make sure you aren’t losing fuel another way. Old gas can also gunk up a fuel line, so old gas plus a grimy fuel line often go hand in hand.

divider 1 Engines Only Need These Three Things

Small engines only need three components to run properly: sparks, air, and fuel. As long as your engine has a spark, plenty of clean flowing air, and the proper fuel, there is no reason it should not be running. A stall is an indication that one of these three things is being prevented or impeded. Most of the suggestions on this list revolve around these three key components.

If you have tried these suggestions and you are still running into persistent stalling problems, then there could be something more seriously wrong with your engine that might need professional help.

man in blue shirt mowing a lawn
Image Credit: Edwin Chen, Unsplash

What To Do If Your Engine Keeps Stalling

If your engine continues to stall after doing everything you can at home, there might be a bigger issue at play. Things can break in a lawn mower engine that could cause a stall. There could be wear, corrosion, erosion, cracks, or dents that impede the proper functioning of your engine.

These issues might need the help of a small engine technician to identify and resolve. If your mower continues to stall out and you can’t find a reason, try taking it in to be looked at. In most cases, the problem will lie with one of these common issues surrounding the flow of sparks, fuel, and air.

divider 7 Conclusion

Lawn mower stalls can be even more frustrating than starter problems. Having your mower cut out in the middle of a job can be extremely irritating. Lawn mower engines that stall generally have an issue with power, fuel, or airflow. Diagnosing the problem and crafting a solution is key to ensuring your lawn mower keeps running time and again without issue.

Featured Image Credit: Piqsels


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